1. Field of the Invention
The present invention generally relates to molding of plastic containers from preforms. More particularly, the invention relates to the control of the liquid stream that is injected into the preform during hydraulic blow molding.
2. Description of Related Art
Plastic containers are commonly used for the packaging of various products, including liquid (including viscous) products. One common type of plastic container is the blow molded plastic container, which is often formed of a polyester material, and more specifically, polyethylene terephthalate (PET). Blow molded plastic containers are typically formed by placing a heated preform into a blow mold and then blowing and inflating the preform with air until the preform contacts the interior surfaces of the mold cavity, which define the final shape of the desired container. Once the inflated preform has been held against the interior surfaces of the mold cavity by the pressure of the blow air for a length of time sufficient to “freeze” the plastic, the blow molded container is removed from the mold.
In traditional blow molding, after the heated preform has been introduced into the mold cavity, a stretch rod is often advanced within the preform to initiate longitudinal stretching of the preform before any significant radial expansion of the preform is undertaken by the introduction of blow air. The stretch rod will typically remain within the preform during radial expansion, and is retracted prior to removal of the container from the molding machine.
The blow molded containers are then transported to the location where the containers will be filled with the intended product. This may include the packaging and shipping of the containers to a remote location or may involve the transfer of the containers to a local facility, where these final steps occur before being shipped to a retailer or end-user.
With the above method, blow molding and filling are distinct and separate steps in the process of producing a product filled container. A newer process involves the use of the end product in the molding of the container. Instead of utilizing air as a blowing medium, this new process utilizes a liquid, and more specifically the actual end product being packaged in the container and sold to the end consumer, as the container's molding medium. As used herein, this type of molding is referred to as hydraulic blow molding.